Understanding Low-Frequency Dynamics with Terahertz (THz) Spectroscopy

Terahertz (THz) spectroscopy is another powerful tool we use to study the collective dynamics of liquid crystals. When exposed to THz radiation, liquid crystals exhibit low-frequency vibrational modes, which can be studied to understand how these materials respond to external stimuli. In particular, we are investigating how the electronic and molecular structures of liquid crystals evolve across phase transitions, from isotropic liquids to liquid crystal and solid phases.

Recent studies have shown that ultrafast changes in the refractive index of liquid crystals occur on femtosecond timescales due to electronic excitations. These excitations relax through coherent molecular vibrations, which modulate the material’s birefringence at frequencies in the few THz range.

By using THz pump-optical probe setups, we can investigate how molecular dynamics in liquid crystals differ from the behavior of individual molecules. Our research addresses several key questions:

• How do collective molecular motions in liquid crystals differ from single-molecule dynamics?

• Can resonant collective dynamics influence the material's electronic and structural properties?

• What are the mechanisms behind THz radiation absorption in liquid crystals, and how do they vary across the 1–10 THz range?

• Can we induce phonon-like excitations in liquid crystals?

This detailed examination of low-frequency dynamics in liquid crystals provides deeper insights into their collective behaviors and enables us to understand and control their structural and electronic properties, particularly during phase transitions and under external influences.